When George Zimmerman shot Trayvon Martin, anti-rights politicians and media saw an opportunity to sway public opinion in favor of repealing state "castle doctrine" laws. All they needed was supportive “research.”

Enter Cheng Cheng and Mark Hoekstra, both of the Texas A&M University Economics Department -- they published a paper titled “Does Strengthening Self-Defense Law Deter Crime or Escalate Violence? Evidence from Expansions to Castle Doctrine.” They concluded that "castle doctrine" had no beneficial impact on burglary, robbery, and aggravated assault. They also claimed that the result of “strengthening self-defense law is increased homicide.” Their conclusion: enhanced self-defense laws caused more murder.

Had the media actually explored available data themselves, Cheng and Hoekstra’s research would have been marginalized instead of lauded as evidence that "castle doctrine" should be repealed.

What is "castle doctrine"?

"Castle doctrine" laws include three possible enhancements to existing self-defense laws. First: if people are someplace they have the right to be, they’re no longer obligated to attempt flight before using defensive force (Remove Duty to Retreat, also called Stand Your Ground). Second: if attacked, it’s reasonable for the defender to believe their life is at risk (Presumption of Reasonable Fear). Third: it’s much harder for attackers or their estate to sue for damages resulting from justifiable self-defense (Civil Liability Protection).

Not all "castle doctrine" states enact all three enhancements, nor do they necessarily enact them all at once. For example, Alaska had already enacted the second and third enhancements prior to removing the duty to retreat.

Authors’ dataset contains errors and inaccurate assumptions

Cheng and Hoekstra recently published an updated version of their research, yet the authors retained numerous errors from their earlier version, calling into question their methods and motives.

Cheng and Hoekstra compiled a table of 20 states that enacted some or all of these "castle doctrine" laws between 2000 and 2010, but 24 states enacted "castle doctrine" laws during their study period [page 36].

They claimed that Missouri enacted Stand Your Ground and civil protection, but Missouri law includes limited enhancements and shouldn’t be counted. Even so, their dataset contained many other errors. For example, they claimed 17 states removed the duty to retreat during their study period -- actually, 19 did. Twenty-two states provide civil liability protection -- the authors included only 17 (see graph below). They correctly noted that 13 states enacted Presumption of Reasonable Fear, but they ignored four states that enacted "castle doctrine" laws: Idaho (2006), Maine (2007), Wisconsin (2008), and Wyoming (2008).

Another problem with their dataset is that they equate Stand Your Ground with "castle doctrine":

In 2005, Florida became the first in a recent wave of states to pass laws that explicitly extend castle doctrine to places outside the home, and to expand self-defense protections in other ways. Since then, more than 20 states have followed in strengthening their self-defense laws by passing versions of “castle doctrine” or “stand-your-ground” laws. ... For ease of exposition, we subsequently refer to these laws as castle doctrine laws. [page 1]

As shown later in this article, the difference between enacting only Stand Your Ground and full "castle doctrine" is significant when looking at crime trends.